In a variety of subsea well applications, a subsea test tree is deployed into subsurface equipment to enable subsea well control during completion operations, flow testing operations, intervention operations, or other subsea well operations performed from a surface facility, such as a floating vessel. For example, the subsea test tree may be used within a subsea blowout preventer to control fluid flow. Depending on the subsea operation, various types of well equipment, e.g. coiled tubing or wireline, may be deployed through the subsea test tree via an interior passageway. The subsea test tree also comprises several valves, including valves which fail to a closed position to secure the wellbore if hydraulic control pressure is lost. However, if the hydraulic control pressure is lost when the well equipment is disposed in the interior passageway, difficulties can arise with respect to shearing equipment, e.g. coiled tubing, to enable closure of the failsafe valve. Some failsafe valves are in the form of ball valves which close under the force of a mechanical spring. However, the mechanical spring tends to provide insufficient force for shearing coiled tubing and other types of equipment.